Erosion-corrosion of 304N austenitic steels in liquid PbBi flow perpendicular to steel surface

Highlights: • Corrosion performance was characterized by XRD, SEM, EBSD, TEM and Raman methods. • High density perpendicular LBE flow results in surface plastic deformation of steel. • Perpendicular LBE flow accelerates local breakaway oxidation. • Crack across the degraded subsurface facilitated LBE penetration and dissolution. In this paper, corrosion performance of 304N austenitic stainless steel with 0.17 wt.% nitrogen was studied in flowing oxygen-saturated lead bismuth eutectic (LBE) at 400 °C. Perpendicular flow pattern was introduced to steel surface, on which various corrosion behaviors, i.e. oxidation, erosion, and dissolution, were simultaneously detected even at a low fluid rate of ~1 m/s after 1000 h. This allowed an investigation into their synergistic effects. Besides, degradation in chemical compositions and mechanical properties was profoundly identified within steel subsurface by means of multi-scale characterization. Role of subsurface degradation in different corrosion failure modes was then elucidated. With regard to breakaway oxidation, an interesting mechanism was proposed for this essential feature of austenitic steels. Plastic deformation microstructure within perpendicularly eroded austenitic steel subsurface, confirmed in other flowing corrosive media, was revealed in liquid LBE flow for the first time and explained in terms of stacking fault energy. Crack across the degraded steel subsurface was proven to be responsible for LBE penetration and selective dissolution attack on steel matrix.